Multimedia content, such as video playback, live streaming, online interactive gaming, file delivery and mobile TV, is seen as the key driver for data traffic demand on wireless cellular networks. Multimedia content to a large number of users can be distributed by unicast, broadcast and multicast. In the following, the term “multicast” is used to include “broadcast” and vice versa. Unicast is a dedicated bidirectional point-to-point link for transmission between the base station and one user mobile device. Evolved Multimedia Broadcast Multicast Service (eMBMS) is an LTE technique offering a specific broadcast bearer to deliver data content to multiple users over shared downlink resources, which is more efficient than dedicating a unicast bearer for each user. Multicast-broadcast single-frequency network (MBSFN) further improves spectral efficiency by dynamically forming single-frequency networks whereby a mobile terminal (in LTE, the UE) can seamlessly receive the same content over eMBMS from multiple base stations (in LTE, the eNodeB) within a MBSFN area. A single-frequency network comprises groups of adjacent eMBMS base stations at which the same signal is synchronized and broadcast simultaneously on the same MBSFN sub-carrier frequencies and time-slots. The combination of eMBMS transmission from multiple base stations in a MBSFN service area provides a degree of transmission robustness in the form of spatial transmit diversity and effectively eliminates internal cell edges. However, a problem exists in handling the transfer of a mobile terminal between different MBSFN areas and between MBSFN and reserved unicast cells. A similar a problem exists in handling the transfer of a mobile terminal between eMBMS cells. Seamless mobility of the mobile terminals across an LTE network with different MBSFNs is not supported in 3GPP, so that service interruption may result, i.e. due to delays at the cell-edges while the mobile terminal acquires information about the targeted area or cell. Service interruption may also result when a the mobile terminal moves from a MBSFN providing an eMBMS broadcast service to a MBSFN where the service in question may only be available by unicast.
eMBMS and MBSFN basics are described in 3GPP TS 123.246 Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description (Release 9), V9.5.0 (2010-06); the 3rd Generation Partnership Project (http://www.3gpp.org).